Lifting mechanism



Feb. 10, 1953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Shee ts-Sheet 1 IN VEN TOR.

X J MAzT,

BY 6 YW Q K,

4 77'0ENEYS Feb. 10, 1953 R. HASTINGS, JR 2,627,943

- LIFTING MECHANISM Filed NOV. 29, 1951 4 Sheets-Sheet 2 I INVENTOR. [II, FIG. 5. BY

Feb. 10, 1953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Sheets-Sheet 3 1 Mimi? m a Ine-// X INVENTOR. mu M7} BY )1 6 7w 7 014;

4TTOP/VfYS Feb. 10, 1.953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Sheets-Sheet 4 FIG. 8.

Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE LIFTING MECHANISMRussell Hastings, Jr., Wellesley Hills, Mass., as-

signor to Lewis-Shepard Company, Watertown, Mass, a corporation ofMassachusetts ApplicationNovember 29, 1951, Serial No. 258,791

13Claims. 1

This invention relates to improvements in an existing type of liftingmechanism occasionally employed in the construction of industrial lifttrucks, stackers and like devices for elevating, stowing, transportingand otherwise handling merchandise and various articles of manufactureand parts thereof. In the type of mechanism referred to, the merchandiseor other articles to be elevated are picked up by or deposited in aload-carriage vertically movable on an upright which is itselfvertically movable on a stationary upright secured to the base of themechanism and generally referred to as a mast. The lifting means inexisting mechanisms of this type generally comprises a single hydraulicram, a pair of chains each attached to the load-carriage at one end andat the other end to the plunger of the ram, and a number of idlers orsprockets around which each chain is successively passed in such mannerthat, when the ram is actuated, the load-carriage is first raised to thetop of the movable upright at three times the speed at'which the ramplunger moves, and then the movable upright itself, together with saidcarriage, is elevated at the same relative speed along the mast.

As mechanism of this type has been constructed heretofore, its operationhas not been wholly satisfactory because of a lack of smoothness in themovement of the load-carriage; instead of being smooth and even themovement would be jerky. This irregular movement is in effect avibratory motion with a slow vibration rate of about two or three cyclesper second. It may be initiated by any minute irregularity in theguideways of the uprights sufficient to cause a very slight increase offriction .between the operating parts; and it also may be initiated ineither chain by the action of that chain in passing over an idler orsprocket, and once startedmay become more intense because of thecombined effect of the elasticity in a long lifting chain and thevariable friction in the operating members.

The object of the present improvements is to provide mechanism of thetype aforesaidwhich, in operation, will be substantially free of theseirregularities, to the end that the movement of the load-carriagecontinuously from its loading position to its discharging position andviceversa may be smooth and regular.

In practising my invention, I employ chains having articulate linksrather than any other form of cable for reasons which it is notnecessary to explain here. Hence, though in describing and illustratingmy improvements I specifically refer to the use of chains as such, I donot wish to be understood as excluding the otheriforms of cables.

As shown in'the 'accompanying-drawings, mechanism of the type aforesaid.and containing my improvements is incorporated in an industrial lifttruck whereof Fig. l is a perspective view showing the load-carriageraised to the top of the inner frame. Fig. 2 isa-front elevation;Figs..:3, i and '5 are elevations on a plane indicated-by-the line "lliinFig. 2, Fig. 3 showing the carriage in its leading position, Fig. 4showing the carriage raised to the top of the inner frame, and Fig. 5showing, the carriage and inner frame raised on the mast; Figs. 6, 7 and8' are explanatory :d-iagrams; and Fig. 9 is a detail view on a largerscale showing the. ram plunger and its associated parts.

The mast ID which, as shown here, comprises a pair of upright channelbars firmly braced together to form a frame-like structure, is securedto a base H which, in case the mechanism is mounted on a truck, as here,maybe the truckbody. The channels of the mast face each other so as toprovide guides for an inner frame or upright 52 which may likewise becomposed of channel bars with their channels facing each other. Thisinner frame is fitted to the mast so as to be movable longitudinallythereof. The load-carriage !3 which, as here shown, is of theconventional forked-type customarily used in industrial lift trucks,stackers :and other related mechanisms, is fitted to the inner frame-soas to be movable longitudinally thereof while guided by the channels ofthat frame. To reduce. :friction, the parts guided by the-channelsmayvhe provided with the customaryrollers .(not: shown).

Each chain of the pair ['5 is of equal length and operativelyconnectedat one :endto the loadcarriage, thence passed successivelyaround four idlers or sprockets and operatively attached at its otherend to a crosshead 116 mounted on the plunger ll of a ram the cylinder18 of which is secured to the base ll. Thev four :idlers for one of thechains and the four for the-otherchai-n together comprise four pairs ofsprockets the respective pairs of which are denoted byt'he numerals I9,20, 2! and 22, and both sprockets of any pair are identical in structureand dimensions. The pair iii is journaled on and near the top of theinner frame [2, the pair 2 0 on and near the bottom of that frame, thepair 2 l in bearing supports it depending from the crosshead I6, and thepair 22 in bearing supports '23 attached to the base H by anchor rods14. The four sprockets over which one of the chains is looped lie in asingle plane, the four over which the other chain is looped lie in aplane parallel to the first, and each chain runs, as shown, from the endthereof which is operatively attached to the load-carriage to and overone of the sprockets l9, thence in succession to and around one of eachof the sprockets of the respective pairs 29, 2| and 22, and thence tothe crosshead (6 to which its other end, as already stated, is attached.

I have observed that a contributing cause of the irregularities in theoperation of the prior mechanisms of this type is the fact that all theruns of the chains did not lie parallel each to each and to the plungerof the ram; for I have found that by selecting idlers or sprocketshaving such relative dimensions that all the runs of the chains will bedisposed in parallel relation to the plunger, said contributing causemay be removed. To this end, therefore, I use sprockets for the first,second and third pairs, i9, 26 and 2| respectively, having such relativepitch diameters that the pitch diameter of a sprocket of the second pair20 plus the pitch diameter of a sprocket of the third pair 2| will beless than the pitch diameter of a sprocket of the first pair 19; and Imake the pitch diameter of each sprocket of the fourth pair 22 less thanthe pitch diameter of each sprocket of the third pair 2|; in addition Isecure the crosshead [6 to the ram plunger I! in such positionrelative-thereto, and attach the dead ends of the chains at such points24 on the bearing supports I6 secured to the crosshead, that thedistance (Figs. 4 and 9) from the longitudinal central line 25 of theram to a line connectin the points 24 will be equal to (Zr-R) where r isthe radius of a sprocket of the fourth pair 22, and R the radius of asprocket of the third pair 2|. When the sprockets have these relativedimensions and the crosshead is mounted on the plunger in the positionjust defined, all the runs of the chains will lie parallel to each otherand to the plunger of the ram and the mechanism will be more evenlybalanced than hitherto. This arrangement, as I have found, will conduceto the smoothness of operation of the mechanism, provided the size ofeach of the idlers or sprockets is such that the pitch line of each isequal to an even number of pitch lengths of the chains; for unless thiscondition obtains, the chordal action of the chains, when pa sing overan idler r sprocket, will tend to develop a vibratory motion since thedistance from the center or pitch line of the chain to the center lineof the sprocket is continually changing. To

illustrate this chordal action, and how I prevent it from developing anirregularity in the movement of the chains, reference may be had to thediagrams of Figs. 6, 7 and 8. In these three diagrams, for the sake ofillustration, the size of the sprocket S there shown is reduced to apitch line of only four chain pitch lengths (a pitch length on the scaleof these diagrams being the distance between the pitch points marked 23and 30). These diagrams show that if the two lengths of the chain whichdepend from each side of the sprocket S are parallel and if the pitchline of that sprocket is equal to the sum of an even number or chainpitches, a uniform linear motion of one end of the chain will produce anequal and constant linear motion of the other end of the chain becausethe moment arm or distance from the center of the chain depending fromone side of the sprocket to the center of the sprocket will at all timesbe equal to the corresponding moment arm at the other side of thesprocket. For example, as shown in Fig. 7, when the sprocket has rotated22 /2 from the point P in Fig. 6, the effective moment arm at each sideof the sprocket will have been reduced from the original distance B(Fig. 6) to a new distance .92R (Fig. '7) both of these equal momentarms giving a balanced condition. Again, when the rotation hasprogressed to (Fig. 8) the corresponding moment arms will become .71R oneach side of the sprocket. In the example just referred to the two runsof the chain from the sprocket S are parallel and the pitch line of thesprocket is equal to an even number of pitches of the chain. With bothof these conditions met, a uniform linear motion is provided when thechain passes over a sprocket.

As each successive pitch point first reaches and is engaged by asprocket or idler, the corresponding pin of the chain starts to rotatethrough a few degrees, and this rotation continues until the next pitchpoint engages the sprocket or idler. Inasmuch as starting friction isgreater than running friction, this tends to impart a slight jerk to thechains. Such jerk, because it is very slight, is inconsequential byitself, but if the chains are arranged so that a jerk occurssimultaneously in both chains, it is more likely to initiate a vibratorymotion in the entire suspension especially if the frequency of thesejerks is harmonically related to the natural period of vibration of theentire suspension, whereby a succession of slight jerks may develop intoa substantial vibration. To prevent such jerks from occurringsimultaneously in both chains, I make the connecting link 3! (Fig. 2) inwhich one of the chains terminates and through which that chain isoperatively attached to the load-carriage, longer, by one-half a chainpitch, than the connecting link 32 by which the other chain isoperatively attached to the load-carriage; and the lengths of theconnecting links 33 and 34 (Fig. 2) by which the other ends of thechains are operatively attached to the crosshead 16, also differ byone-half a chain pitch. In this way each chain, so to speak, takes turnwith respect to the engagement of its links with the respectivesprockets or idlers over which they operate, and thus insures that thesuccessive jerks of one chain will alternate with those of the other.

In addition, I provide an equalizer bar 21 which is interposed betweenthe chains and the load carriage and to which the latter is pivoted at23.

This bar not only insures that the tension on each chain will always bethe same and centralizes the liftin force on the carriage, but alsoreduces, by its lever action, the magnitude of the jerks from eachchain.

In practice I may fix the respective sizes of the sprockets as follows:I first determine the pitch line length, in terms of an even number ofchain pitches, of the smallest size sprocket it is practicable to use.Assuming that for mechanism of a given capacity the pitch line length ofthe smallest size sprocket suitable for use is equal to fourteen chainpitch lengths, I use a sprocket of that size for the sprockets 22 andpreferably also for the sprockets 20. Then for the sprockets 2! I usesprockets having a pitch line length equal to eighteen chain pitchlengths; and for the sprockets I9 I use sprockets having a pitch linelength of thirty-six chain pitch lengths. In a case where the respectivesizes of the sprockets are determined in this manner and the sprockets22 and 20 are of equa1 size and that size taken arena-43 5 as a unit orbase, the size of the sprockets 2| will be greater than the sprockets 22and the sprockets l9 twice the size of the sprockets 2|. But of courseother relative sprocket sizes may be adopted in practising myimprovements.

By the diagrams of Figures 6, '7 and 8 where, as shown, the chainsdepending from a sprocket or idler are parallel and the pitch line ofthe sprocket is equal to an even number of chain pitches, I have shownwhy under these conditions the mechanism will be evenly balanced.Referring again to those diagrams, it will be noted that at the pitchpoints of each depending chain the latter is tangent to the pitchcircumference of the sprocket r idler at the same instant, as shown inFig. 6. In the more general case, where the depending chains are notparallel, it will be obvious that the mechanism will also be evenlybalanced provided that the relation between the pitch diameter of thesprocket or idler and the chain pitch is such that each dependent end ofthe chain will be tangent at its pitch points to the pitch circumferenceof the sprocket or idler at the same instant.

In operation: when the ram is actuated the load-carriage will be raisedfrom its loading position (Fig. 3) to the top of the inner frame (Fig.4) at three times the speed with which the plunger moves, while theinner frame will remain stationary. When the carriage reaches the top ofthe inner frame, its movement on the inner frame will be checked by theupper crossmember of the inner frame; then, as the plunger continues itsupward movement, the inner frame together with the carriage will move upthe mast (Fig. 5) without any break in the continuity of the movement ofthe carriage, or its speed, from its loading. position to itsdischarging position wherever the latter may be. The reason why theinner frame will remain stationary while the carriage is being raised tothe top of the inner frame is that the load on the ram when the innerframe moves is greater by the weight of that frame than when the ramlifts the carriage alone. Heretofore, in mechanisms of this type it hasinvariablybeen necessary to provide means to latch the inner frame tothe mast during the lifting of the carriage to the top of the innerframe, since the latter, but for the latch, would frequently, if notalways, begin its movement prematurely. Since this is due either :topoorly balanced conditions within prior mechanisms of this type, or tothe development therein of one or more of the irregularities pointed outabove, or to both these causes, the utility of my improvements whichremove these causes will be appreciated. Nevertheless the use of myimprovements together with such latching means, should that beconsidered desirable for any reason, would still be within the scope ofmy invention.

In illustrating and describing the type of mechanism in which myimprovements are to be incorporated, I have shown and described the ramas having its cylinder [8 secured to the base H. In such case themovable member of the ram will be its plunger l1. But since it is notunusual, in hydraulic lifting mechanism, to mount the ram so that itscylinder will be the movable member and its plunger the stationarymember, I wish it understood that my improvements are applicable tomechanism of the type referred to irrespective of how the ram is mountedtherein. I also wish it understood that while I prefer for practicalreasons to use chains of articulate links 6 rather than other forms ofcables in practising my improvements, I do not consider thatthesubstitution of other forms of cables for the chains as such, removesthe mechanism from the scope of my invention.

I claim-as my invention:

1. In a lifting mechanism of the type described which comprises a mastsecured to the base of said mechanism, an upright fitted to and mmablelongitudinally of the mast, a load-carriage fitted to and movablelongitudinally of said .upright, a ram the stationary member of which.is secured to said base, a pair of equidiameter idlers journaled on andnear the top of said upright, a second pair of equidiameter idlers'journaled on and near the bottom of said upright, a third pair ofequidiameter idlers journaled on the movable member of the ram, a fourthpair of equidi-ameter idlers the journal supports of. which are attachedto said base, a pair of cables of equal length each of which isoperatively-connected at one end to the load carriage, thence passedsuccessively to and around an idler of the first, second, third andfourth pairs respectively and thence to the movable member of the ram towhich 'its other end is operatively connected, the improvement in theaforesaid mechanism which consists in this, namely, that the sum of thepitch diameters of an idler of the second pair and an idler of the thirdpair is less than the pitch diameter of an idler of the first pair, thatthe pitch diameter of an idler of the fourth pair is less than the pitchdiameter of an idler of the third pair, and that the distance betweenthe longitudinal center line of the ram and .a line connecting thepoints where the cables are at,- tached to the ram is equal totwo-thirds of the difference between the diameter of an idler of thefourth pair and the radius of an idler of the third pair.

2. The improvement defined in claim 1 wherein the movable member of theram is its plunger and the stationary member is its cylinder, andwherein said cylinder is secured to the base of said mechanism and thecables operatively connected to said plunger.

3. The improvement defined in claim 1 wherein an equalizer bar isinterposed between the cables and the load-carriage and to which theload-carriage is pivotally connected.

The improvement defined in claim 1 wherein the pitch diameters of eachof the idlers. of the second and fourth pairs are equal, the pitchdiameter of each idler of the third pair twosevenths greater than thepitch diameter of .an idler of the fourth pair, and the pitch diameterof each idler of the first pair twice the pitch diameter of an idler ofthe third pair.

5. In a lifting mechanism of the type described which comprises a mastsecured to the base of said mechanism, an upright fitted to and movablelongitudinally of the mast, a load-carriage fitted to and movablelongitudinally of said upright, a ram the stationary member of which issecured to said base, a pair of equidiameter idlers journaled on andnear the top of said upright, a second pair of equidiameter idlersjournaled on and near the bottom of said upright, a third pair ofequidiameter idlers journaled on the movable member of the ram, a fourthpair of equidiameter idlers the journal supports of which are attachedto said base, a pair of cables of equal length each of which isoperatively connected at one end to the load-carriage, thence passedsuccessively to and around an idler of the first, second,

third and fourth pairs respectively and thence to the movable member ofthe ram to which its other end is operatively connected; the improvementin the aforesaid mechanism which consists in this, namely, that the pairof cables comprises two chains each of articulate links and having thesame pitch, and that the pitch circumference of each idler isapproximately equal to the sum of an even number of pitch lengths of thesaid chains.

6. The improvement defined in claim wherein an equalizer bar isinterposed between the chains and the load-carriage and to which saidcarriage is pivotally connected.

7. The improvement defined in claim 5 wherein the diameters of each ofthe idlers of the second and fourth pairs are equal, the pitch diameterof each idler of the third pair two-sevenths greater than the pitchdiameter of an idler of the fourth pair, and the pitch diameter of eachidler of the first pair twice the pitch diameter of an idler of thethird pair.

8. In a lifting mechanism of the type described which comprises a mastsecured to the base of said mechanism, an upright fitted to and movablelongitudinally of the mast, a load-carriage fitted to and movablelongitudinally of said upright, a ram the stationary member of which issecured to said base, a pair of equidiameter idlers journaled on andnear the top of said upright, a second pair of equidiameter idlersjournaled on and near the bottom of said upright, a third pair ofequidiameter idlers journaled on the movable member of the ram, a fourthpair of equidiameter idlers the journal supports of which are attachedto said base, a pair of cables of equal length each of which isoperatively connected at one end to the load-carriage, thence passedsuccessively to and around an idler of the first, second, third andfourth pairs respectively and thence to the movable member of the ram towhich its other end is operatively connected; the improvement in theaforesaid mechanism which consists in this, namely, that the pair ofcables comprises two chains each of articulate links and having the samepitch and terminating in connecting links for operatively connecting therespective chains to the loadcarriage at one end and to the movablemember of the ram at the other end, the lengths of the connecting linksadjacent to the load-carriage differing from each other by one-halfachain pitch, and the lengths of the connecting links adjacent to themovable member of the ram also differing from each other by one-half achain pitch.

., 9. The improvement defined in claim 5 wherein each chain terminatesin connecting links for operatively connecting the respective chains tothe load-carriage at one end and to the movable member of the ram at theother end, the lengths of the connecting links adjacent to theloadcarriage diifering from each other by one-half a chain pitch, andthe lengths of the connecting links adjacent to the movable member ofthe ram also differing from each other by one-half a chain pitch.

10. The improvement defined in claim 8 wherein an equalizer bar isinterposed between the chains and the load-carriage and to which saidcarriage is pivotally connected.

11. In a lifting mechanism of the type described which comprises a mastsecured to the base of said mechanism, an upright fitted to and movablelongitudinally of the mast, a load-carriage fitted to and movablelongitudinally of said upright, a ram the stationary member of which issecured to said base, a pair of equidiameter idlers journaled on andnear the top of said upright, a second pair of equidiameter idlersjournaled on and near the bottom of said upright, a third pair ofequidiameter idlers journaled on the movable member of the ram, a fourthpair of equidiameter idlers the journal supports of which are attachedto said base, a pair of cables of equal length each of which isoperatively connected at one end to the load-carriage, thence passedsuccessively to and around an idler of the first, second, third andfourth pairs respectively and thence to the movable member of the ram towhich its other end is operatively connected; the improvement in theaforesaid mechanism which consists in this, namely, that the pair ofcables comprise two chains each of articulate links and having the samepitch and the relation between the pitch diameter of each idler and thechain pitch being such that each end of the chain depending from anidler will be tangent to the pitch circumference of the idler at bothpitch points at the same instant.

12. In a lifting mechanism of the type described which comprises a mastsecured to the base of said mechanism, an upright fitted to and movablelongitudinally of the mast, a load-carriage fitted to and movablelongitudinally of said upright, a ram the stationary member of which issecured to said base, a pair of equidiameter idlers journaled on andnear the top of said upright, a second pair of equidiameter idlersjournaled on and near the bottom of said upright, a third pair ofequidiameter idlers journaled on the movable member of the ram, a fourthpair of equidiameter idlers the journal supports of which are attachedto said base, a pair of cables of equal length each of which isoperatively connected at one end to the load-carriage, thence passedsuccessively to and around an idler of the first, second, third andfourth pairsrespectively and thence to the movable member of the ram towhich its other end is opertaively connected; the improvement in theaforesaid mechanism which consists in this, namely, that the pair ofcables comprises two chains each of articulate links and having the samepitch and so disposed that the links of one chain are in staggeredrelation to the links of the other chain.

13. The improvement defined in claim 5 wherein the chains are sodisposed that the links of one chain are in staggered relation to thelinks of the other chain.

' RUSSELL HASTINGS, J R.

No references cited.

